The long term goal of this proposal by the Ontario Family Registry (OFR) is to participate as part of the CFRBCS to complete the establishment of a hypothesis-driven interdisciplinary research platform to support, expedite and implement research in genetic epidemiology of breast cancer. The OFR contains a population-based cohort of breast cancer cases, identified as incident cases from the Ontario Cancer Registry from 1996 to 1998, and their families. In addition, the OFR contains prevalent AJ cases and their families recruited at familial cancer clinics. We have developed an extensive system for the identification of population-based incident breast cancer cases and the collection of family history, epidemiologic information, blood, and tissue specimens. The specific aims of the renewal of the ORF are: 1) To enhance the value of the OFR by completing the collection of data and biospecimens from probands, extending the collection of data and biospecimens from relatives and recruiting additional subjects (minorities and Ashkenazim Jewish) into the OFR 2) To maintain a functioning OFR database and biospecimen repository 3) To participate in a broad spectrum of scientific studies, including clinical, pathological, gene discovery, gene-environment, genetic modifiers, and psycho-social. 4) To provide a resource for collaborative studies involving the CFRBCS sites and external collaborators This information will lead to an improved understanding of the contributions made to the etiology of breast cancer by genetic and environmental factors, to identify the factors, responsible, and to gain an understanding of how they act, both separately and together, to influence breast cancer risk.